Technical Field
This application relates generally to battery chargers for use with electric vehicles or other battery powered devices, and more specifically to a bidirectional battery charger integrated with renewable energy generation.
Background Information
In the past decade, there has been a significant increase in the use electric vehicles and other types of battery powered devices. Together with this increase there has been a similar increase in the use of battery chargers. In the case of electric vehicles, battery chargers have often taken the form of Level 1 or Level 2 alternating-current (AC) slow chargers. Such slow chargers typically utilize about 1.8 kilowatts (kW) in the case of Level 1 chargers, and 7.2 kW in the case of Level 2 chargers, of grid-supplied power. Some attempts have been made to produce AC fast chargers with high efficiency. Such fast chargers may utilize about 11 kW of power.
Regardless of type, the power t used by most battery chargers has typically been grid-supplied, without contribution from any local renewable energy generation (e.g., solar panels, wind turbines, geothermal generator, etc. that may be located nearby the charger). When renewable energy generation has been used alongside battery chargers, such systems have typically been totally isolated from each other, leading to high costs, limited control flexibility and lower than desired efficiency.
FIG. 1 is a schematic diagram 100 of a typical isolated arrangement of a battery charger and renewable energy generator. The electrical grid 110 supplies power AC, via inductive element L, to battery charger 120. The battery charger may include (not shown) an alternating current/direct current (AC/DC) rectifier coupled to a mono-directional direct current/direct current (DC/DC) converter. The output of the battery charger is a voltage Vb that may be coupled to a battery (having resistance Rb) of an electric vehicle. Further, a renewable energy generator 130 (e.g., a solar array, wind turbine, geothermal generator, etc.) may supply DC power to a direct current/direct current (DC/AC) inverter 140, and the resulting AC power fed back toward the electrical grid 110.
The use of both a battery charger 120 and a separate DC/AC inverter 140 leads to increased deployment costs. Additional increased costs are often incurred by a need to overdesign the battery charger 120 to deal with power being supplied concurrently from the electrical grid 110 and the DC/AC inverter 140. The separation of the battery charger 120 and the DC/AC inverter 140 prevents any sort of responsive control involving the two components. Finally, the need for DC power originating from the renewable energy generator 130 to first be converted to AC power (via the DC/AC inverter 140) before it is then converted back to DC power (via the battery charger 120) leads to low system efficiency.
What is needed is a bidirectional battery charger (e.g., for an electric vehicle) that is integrated with renewable energy generation, which may address some or all of the shortcomings of prior designs.